Most international flights arrive at Houari Boumediene Airport in Algiers, the country's main hub. Oran and Constantine also have international airports with flights from France, Spain, Turkey, and other North African countries.
Air Algerie is the national carrier and operates most routes, with frequent connections to Paris, Marseille, Lyon, and other French cities. Air France, Transavia, Tunisair, and Turkish Airlines also serve Algeria. Flights from France are the cheapest and most frequent, given the large Algerian diaspora there.
From neighboring countries, you can cross overland from Tunisia at several border points -- the crossing near Annaba is the most straightforward. The Moroccan border has been closed since 1994 and remains so. Southern land borders with Mali, Niger, and Libya are either closed or extremely inadvisable due to security concerns.
Ferries connect Algiers, Oran, Bejaia, and Skikda with Marseille, Alicante, and Barcelona. Algerie Ferries and Corsica Linea operate these routes. The Marseille-Algiers crossing takes about 20 hours and is popular with Algerian families, especially in summer. Book well ahead for July and August.
You need a visa to enter Algeria, and the process is not quick. Apply at your nearest Algerian consulate well in advance. You will need an invitation letter or hotel booking, and processing can take several weeks.